Process for preparing a catalyst of a silver-base alloy



United States Patent PROCESS FOR PREPARING ACATALYST OF A SILVER-BASE ALLOY Barbara McPhee Burford, Ottawa, Ontario, Canada, and Adrien Cambron, deceased, late of Ottawa, Ontario, Canada, by The Royal Trust Company, Montreal, Quebec, Canada, executor, assignors to National Research Council, Ottawa, Ontario, Canada, a body corporate N0 Drawing. Application June 5, 1953 Serial No. 359,956

2 Claims. (Cl. 75-173) The present invention relates to improvements in the catalytic oxidation of ethylene to ethylene oxide.

The present invention has for its object the provision of a novel and improved alloy and a novel and improved process for the production of such an alloy for the catalytic conversion of ethylene and other alkenes to ethylene oxide or the corresponding alkene oxide. A further object is the provision of an improved alloy for the production of catalytic bodies which have a high reactivity and selectivity in the catalytic oxidation of ethylene or alkenes to ethylene oxide or the corresponding alkene oxide.

The alloys of the present invention comprise at least about 25% silver, from about 1% to about 75% of one or more alkaline earth metals, such as magnesium, calcium, strontium and barium and a small proportion, from about a trace or 0.01% to the point of saturation of nickel in silver. The nickel is preferably added in the form of a nickel-magnesium alloy containing at least as much and up to times as much magnesium as nickel so that the nickel is homogeneously distributed throughout the remainder of the alloy. Thus the alloy may be prepared by melting the silver and alkaline earth metal and'adding' to the molten metal the required amount of nickel, preferably as a nickebmagnesium alloy containing from 10% to 50% nickel, or the nickel-magnesium alloy may be added to molten silver or to molten alkaline earth metal after which the other component (alkaline earth metal or silver) is added, the whole being heated to a sufiiciently high temperature to insure complete melting of the silver and alkaline earth metal. Thus, where the alloy is to be formed by immersion of a silver sheet in molten alkaline earth metals, such as a mixture of calcium and magnesium, the nickel may be added to the molten alkaline earth metal preferably as the nickel-magnesium addition agent.

The alloys so produced may then be rendered catalytically active in various manners, and may be used as granular particles in a fluidized bed, or adherently bonded to a suitable metal support or in a fixed bed, or may be formed as metal sheets or parts where the catalyst is to be used in the form of a sheet or other thermally conducting part such as a fin in a reaction chamber.

The alloy is treated usually by steaming, followed by boiling in water or dilute acidto render the alloy catalytically active, such processes being fully described in the prior patents to Cambron and McKim Nos. 2,562,857 and 2,562,858 granted July 31, 1951 and National Research Councils Belgian Patent No. 509,882 (patented March 31, 1952).

Referring now in detail to the present preferred and illustrative embodiments of the invention and to the preferred manner of carrying out the process of the present invention, the alloy may comprise from 1% to 75 and preferably from 5% to of calcium metal alloyed with silver to which is added from a trace to 0.4% of nickel and most preferably from a trace to 0.4% nickel by weight of the silver,uniformly distributed throughout the ICC mass of the alloy, theremainder of the alloy being comprised of silver with additions of magnesium, the'magnesium preferably being present in an equal amount to 10 times the quantity of nickel in the alloy.

Preferably, since the melting point of nickel is approximately 1452 C., the nickel is added in the form of a nickel-magnesium binary alloy containing from 10% to 5 0 of nickel, although the eutectic alloy containing 23% nickel is preferred by reason of its lower melting point of 507 C., and this binary alloy is added to the molten silver-alkaline earth metal alloy.

Alternatively, the nickel or nickel-magnesium. alloy may be added to molten calcium, strontium or barium, and the silver alloy formed by momentary immersion of a silver sheet or silver coated sheet in the molten alkaline earth metal whereby the nickel containing-silver-alkaline earth metal-alloy is formed on the silver surface of the sheet and is bonded therewith, the surface of the alloy being enriched'with silver by annealing the alkaline earth metal coated sheet until the surface of the sheet contains at least 25 silver, after which at least 5% of the alkaline earth metal is removed. although all but a trace of the alkaline earth metal may be removed. The preparation of catalytic alloys by dipping silver coated sheets in molten alka-v line earth metals is disclosed in the prior applications of Wendal A. Alexander, Serial Nos. 334,727 and 334,728 filed February 2, 1953, assigned to National Research Council, Ottawa, Ontario, Canada, a body corporate, and the procedure and techniques there set forth may be closely followed with the addition of from a'trace to 0.4% of nickel or corresponding amounts of the nickel-magnesium alloy to the dipping bath for the metal sheets.

The following are various specific examples of alloys for the catalytic oxidation of ethylene to ethylene oxide, which are also useful in the oxidation of other alkenes and other alkene oxides.

Example 1.An alloyv comprising 89.4% silver, 8.2% calcium and 0.36% nickel was activated in the manner described in the prior patents to Cambron and McKim, and after activation had an analysis of calcium 0.50%, nickel 0.40%, silver 97%. At a reaction temperature of 260 C., and with 15 volumes of air for each volume of ethylene, a total reaction of 93% was attained which included conversion of 45% of the ethylene to ethylene oxide.

Example 2.-In another specimen, the alloy comprised 10.2% calcium and 0.21% nickel before activation and after activation comprised calcium 0.64%, nickel 0.15% and silver 99.21%. Utilizing such a catalyst under the same conditions, the catalyst showed a conversion to ethylene oxide per pass which was considerably higher, and oftentimes as much as 5% higher than was obtained using similar catalysts which excluded nickel from their composition, and even at the end of 100 days of test, catalysts prepared from this alloy demonstrated greater expected life than similar catalysts including no nickel.

Example 3.Rcsults similar to those set forth in the example immediately above were obtained using an alloy comprising calcium 10.0%, nickel 0.15% and the balance silver which, after activation, had an analysis ofcalcium 0.34%, nickel 0.01%, silver 99.65%.

Example 4.A catalytic alloy comprising calcium 1 1.6%, magnesium 2.5%, nickel 0.19% and the balance silver which had been prepared by adding the nickel to a molten alloy of the other elements, the nickel being added in the form of a nickel magnesium alloy containing 23% nickel, after activation had analysis of calcium 0.42%, nickel 0.19%, magnesium 0.0% and the balance silver and showed a yield of 39% ethylene oxide per pass. This same alloy was particularly susceptible to the conditioning treatment following "activation by holding it at about 260 C. than atmosphere of carbon dioxide,

3 after which the activity in converting ethylene to ethylene oxide-had increased to 48%, the desirably high initial activity of the catalyst being attained after four days of reaction whereas without the carbon dioxide treatment the desirably high reaction was attained only after seven days use as a catalyst.

Example 5.-Under similar reacting conditions, a catalyst comprising calcium and 0.36% nickel, and having an analysis, after activation, of calcium 0.66%, nickel 0.40% and silver 98.75% yielded 44% ethylene oxide per pass. A similar catalyst after conditioning at 290 C. for three days in an atmosphere of carbon dioxide, and after being used as a conversion catalyst for four days, produced a yield of 50% ethylene oxide per pass.

Example 6.-- In another specimen, the catalytic alloy had a composition prior to treatment comprising silver 86.5%, calcium 3.7%, barium 9.8% and nickel 0.04% prior to activation and gave good conversionand selectivity in the oxidation of ethylene to ethylene oxide.

Example 7.An example of an alloy which is -lower in silver and is adapted to be applied by dipping to a silver metal sheet or a metal sheet coated with silver, comprises silver 25 calcium 65 nickel 0.10% and magnesium 8%, the nickel being added to the calcium silver alloy by means of a silver magnesium addition agent containing 25% nickel. usual manner and when activated contained only about calcium, 2% magnesium and 0.35% nickel.

Other typical alloys in accordance with the present in vention comprise the following:

Ag, Ca, Mg, Ba, Ni, percent percent percent percent percent In general the foregoing as well as the other alloys are The alloy was activated in the treated until from at least 5% to almost all the alkaline earth metal has been removed from the alloy, so that the alloy becomes activated as a catalyst for the selective oxidation of ethylene to ethylene oxide. The removal of the alkaline earth is preferably by means of a dilute acid, as disclosed in the prior Cambron and McKim patents, which elfects the removal of from 5% to all but a trace of the alkaline earth metal without significant removal of silver from the catalyst material.

The invention in its broader aspects is not limited to the specific steps, processes and compositions shown and described but departures may he made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What is claimed is:

1. The process of preparing a catalyst for the oxidation of ethylene to ethylene oxide which includes preparing an alloy comprising silver, from 1 to calcium, from 0.1 to 0.4% nickel based on the weight of silver, and at least as much magnesium as nickel, the balance of the alloy being essentially silver, and subjecting the alloy to treatment with acid to remove from 5% to all but a trace of the calcium and magnesium content without significant removal of silver, whereby an active catalyst is formed.

2. The process of claim 1 in which the alloy comprises from 5 to 15% calcium, and the magnesium is present in an amount equal to ten times the weight of the nickel.

References Cited in the file of this patent UNITED STATES PATENTS 2,178,454 Metzger Oct. 31, 1939 2,187,379 Hen-sel et a1 Jan. 16, 1940 2,199,458 Hensel et al. May 7, 1940 2,241,816 Hensel et al. May 13, 1941 2,562,858 Cambron et al. July 31, 1951 2,709,173 Brengle et al. May 24, 1955 2,769,016 Lichtenwalter et al. Oct. 30, 1956 

1. THE PROCESS OF PREPARING A CATALYST FOR THE OXIDATION OF ETHYLENE TO ETHYLENE OXIDE WHICH INCLUDES PREPARING AN ALLOY COMPRISING SILVER, FROM 1 TO 75% CALCIUM, FROM 0.1 TO 0.4% NICKEL BASED ON THE WEIGHT OF SILVER, AND AT LEAST AS MUCH MAGNESIUM AS NICKEL, THE BALANCE OF THE ALLOY BEING ESSENTIALLY SILVER, AND SUBJECTING THE ALLOY TO TREATMENT WITH ACID TO REMOVE FROM 5% TO ALL BUT A TRACE OF THE CALCIUM AND MAGNESIUM CONTENT WITHOUT SIGNIFICANT REMOVAL OF SILVER, WHEREBY AN ACTIVE CATALYST IS FORMED. 